1. Field of the Invention
The object of the invention is a device whose function is to significantly reduce the noise produced by a drill when drilling a hole, in a mine, for example.
2. Description of the Prior Art
As a general rule, a drill of this kind is coupled to the driving shaft of a pneumatic or hydraulic hammer which rotates it with a percussive action. The hammer is itself installed on a drilling jumbo carrying a plurality of hammers. The noise created is considerable, reaching and even exceeding 110 dB. It is a cause of irreversible occupational disability, in particular deafness, for persons working in the vicinity.
It is known that there are three main sources of the noise produced by a percussive rotary drill: exhaust compressed air, the drill and the body of the hammer.
The invention relates to a device for attenuating the noise due to the drill. The latter comprises an elongated shaft whose profile in transverse cross-section is more often than not polygonal, or sometimes cylindrical, with a first end part which features a forged collar for coupling it to the hammer and a second end part fitted with a bit of larger diameter than the shaft. The bit may be integral with the shaft or attached to the latter, by means of a screwthread, for example.
In both cases the bit comprises a cutting tip of frustoconical profile of which the larger diameter, that of the end surface with cutting edges, determines the diameter of the drilled hole. To the rear of this end part the bit comprises a cylindrical body whose diameter is significantly larger than that of the shaft.
It has already be proposed to make use of this difference in the transverse dimensions of the shaft and the bit body to soundproof the drill. In the journal "NOISE CONTROL ENGINEERING", volume 15, number 3 of November-December 1980, there is described in an article titled "Noise control of jumbo-mounted percussive drills" a means of soundproofing drills. This consists in a composite sheath fitted over the shaft of the drill over its entire length between the bit and the hammer. This sheath comprises a coating of plastics material with a high molecular weight which covers the surface of the shaft, an elastic intermediate layer of open cell foam and an outside metal tube. At a frequency of 2,000 Hz this device attenuates the noise from a level of 108 dB without the sheath to a value of 101 dB with the sheath.
The principal objective of the invention is to provide a device for attenuating the noise produced by a drill which is at least as effective as the device mentioned hereinabove but the cost of which is significantly reduced and the service life of which is considerably increased.